Influence of lithospheric mantle stratification on craton extension: Insight from two-dimensional thermo-mechanical modeling

Abstract

Lithospheric mantle stratification is a common feature in cratonic areas which has been demonstrated by geophysical and geochemical studies. The influence of lithospheric mantle stratification during craton evolution remains poorly understood. We use a 2D thermo-mechanical coupled numerical model to study the influence of stratified lithospheric mantle on craton extension. A rheologically weak layer representing hydrated and/or metasomatized composition is implemented in the lithospheric mantle. Our results show that the weak mantle layer changes the dynamics of lithospheric extension by enhancing the deformation of the overlying mantle and crust and inhibiting deformation of the underlying mantle. The thickness and depth of the weak layer determines two deformation patterns: 1) narrow mantle necking favored by shallow and thin weak layer, and 2) widespread mantle necking favored by deep and thick weak layer. High Moho temperatures also promote the formation of widespread mantle necking in the model with a weak mantle layer. Both shear heating and plastic strain weakening can enhance deformation and promote asymmetric extension. Modeling results are compared with North China and North Atlantic cratons. Our work indicates that although the presence of a weak layer may not be sufficient to initiate craton deformation, it enhances deformation by lowering the required extensional plate boundary force.